I can't speak definitively about other amplifiers, but I'm assuming results will be the same or similar with other (good) amplifiers as with my TABOO. If so, run... don't walk to your keyboard and place an order for the HDT upgrade kit. Yes, it's that good, and it makes an overall improvement to the sound of the HDT's that is far and away beyond the meager price of the kit, or the 2 hour installation time.

If you also own a TABOO, you're gonna laugh yourself silly when you hear the modded HDT's in TABOO "Lucid mode".

In either mode...

1) expanded sound stage, speakers dissappear more if not completely

2) better detail/microdynamics - I know it's a cliche, but the saying of hearing things in recordings never heard before... it applies in spades here.

:D

P.S. Don't forget to felt the phase-plug as detailed in the HDT tweaks thread.

I have not had the drivers gel waxed yet and am not sure I will. I'm very happy with the way they sound. Steve says the gel wax is supposed to smooth out the "shout" but I don't really hear a "shout" with my room/setup. We'll see after many more hours and days of happy listening

Corey, why do you keep talking about a zbox. I don't see why I would need a zbox. I don't think it would add much to my source and preamp combo.

Alternately for those DIY'ers with a Zen CS as apposed to a TABOO, its likely better for you to build or mod your HDT in the MK-II format instead of the MK-I alternate tuning. The MK-II is 4 ohms which the CS likes. The TABOO likes 6-8 ohms better which the MK-I is.

MK II drivers are rumored to be the following. As for tweeter placement, you'll have to wait until the DecFest and/or release of the MK-II. Unless of course Steve decides to publish that info. The tweeter is fairly well known having been used in the Decware radials. I know the make but not the exact model of the the midbass driver, though it's a fairly easy guess. However, I don't know if it's appropriate at this time to divulge. You'll have to wait for Steve to say or give the OK.

Keep an eye on listeners' comments after the DecFest, or better yet. Go!

I see you you have the Zen CSEX. This amp was optimized for speakers with around 8ohm or higher impedance. This amp is a better match for the HDT MK-I with alternate tuning. The MK-II is a 4ohm speaker designed specifically for use with the original Zen CS (non EX) version. That's not to say that you would not like the MK-II, but I just wanted to point out that you may have less than ideal results. Depending upon your listening habbits you might have clipping, or other problems. You might want to talk to Steve first to confirm.

I'm happy with the alt tuning, but then I also get the tweak bug and I have the sickness of never being completely satified - ie, always looking for ways to get better sound.

Yes, I've thought about trying this combo out, but the 8ohm version of this driver is not very efficient. If I make changes it would be either to stay at my current efficiency range 95-96db or to go higher.

Call me crazy, but one option I'm thinking of trying is using a FE208E sigma and an Aurum Cantus G2si ribbon tweeter.The T/S params on the 208E is similar to the 206E so it should work OK in the HDT cabinet.

This particular combo of drivers is used in Dick Olsher's BassZilla Platinum kit to (reportedly) good effect. I'm thinking the HDT cabinet will do a better job than an open baffle. I bought the kit plans ($23) just to get the crossover design Dick used. I figure it would be a good place to start.

I found some Weldbond glue yesterday and installed the Alternate kit on one HDT.

After evaluation between the regular tuning and alternate tuning it took me about half a song to cut the passives out on the regular tuned slut and install the new passives on that one as well.

This is a fantastic tweak and IMO deserves production status. There is just too much chaos inside the chambers without this foam in there. The sound reflecting back into the rear cone of the FE206-M really messes up the mids and highs.

After a brief glance at your pics on this thread, it has occured to me that you glued your passives on backwards. The large dome should be facing out and should be visible from a front view. This loads the sound into a better dispersion pattern and further radiates sound to the chair with a better disappearing act. Time to get new passives if you are picky, I think it will make a difference.

After looking at the pic in more detail I think I can pin point the problem. The passive was not built correctly. Not a big deal as Decware will promptly ship you out new ones. On mine the big outside surround faces out, then the smaller one is inverted(like the Fostex driver) and the dome is glued to the smaller inverted surround. To have your dome facing out you would have had to glue the big outside surround in an inverted position.

The smaller surround should have been inverted then the dome would be facing out.

To install the ports without having to remove the bracing means sticking the port UP, into the top part of the chamber till it clears the bracing then it will fit down inside.

Also when installing the ports, make sure you have the pipes touching the center line on the coupler. One end usually goes in smoother so attach the coupler to the end that is harder to slide on when it is outside the cabinet. This will leave the easier end of the coupler for pushing onto the existing port inside the HDT. You do not want to break that port free or you are screwed!

I wouldn't worry about making adjustments to the size of foam for the passive chambers although you could split it up the middle and extend past the bracing wood, nearing the port. It probably would be a good idea to keep the foam 2 inches from the port if you are going to go longer than 12 inches.

The adjustments that could be made will be in the driver chamber. Here the foam could be even 5 1/2 inches wide by 19 7/8. This way it would reach the very top piece of foam cut into a triangle and reach down to cover behind the driver. If you are going to do this it would be a good idea to glue the foam so it doesn't make contact with the driver. The driver and passive holes must be notched out precisely if doing this.

Thanks Corey,So are you saying that the driver chamber should be completly covered on all 3 sides with foam from the top of the chamber to the bottom of the driver, with the driver hole and the scalloped passive holes completly cut away?Got any pictures of how yours looked?

Wasn't there any dampening material like felt in those areas to begin with?

I tried lifting, dropping, and walking the passive port extensions in place, but, in the passive chambers, my braces must have been either too wide or too low to allow me to get a straight shot onto the tops of the existing ports. No biggee. I unsrcewed the braces an carefully knocked them out with a hammer.I can reinstal them later.

On a side note:If I can figure out a safe and accurate way to re-route the passive cutouts on the cabinet sides I will mount the new passives with some laser cut rings and screws. The current rabbit cut is only 1/4" wide, but I need closer to 1/2" to accomodate screw holes and tee-nuts. This design would allow the passives to be removable for easier tweeking. Chrome plating the rings would also echo the chrome finish on the phase plugs.

On a side note:If I can figure out a safe and accurate way to re-route the passive cutouts on the cabinet sides I will mount the new passives [/quote]

The way to re-rout would be to start by routing a circle that fits inside the pasive hole then place a larger peace of mdf inside the HDT behind the passive hole and screw that to the circle that you routed. Now you place a larger peace on the out-side of the box, this peace should have a hole in the midle to locate it to the center of the circle that is sitting in side the pasive cut-out. Now you can screw this together and you have 3 peaces that form a sandwich over the passive hole. Now you can fix the routing circle into the middle whole and rout through the top-most layer of the MDF and down into the underlying cabinet.

Hrappur,That sounds like a winner. I can use the same setup for all 4 cutouts. What is the purpose of the mdf panel on the outside of the cabinet? is it to add stability and support or is it for something else that I am missing?Thanks for your help,John

After a brief glance at your pics on this thread, it has occured to me that you glued your passives on backwards. The large dome should be facing out and should be visible from a front view. This loads the sound into a better dispersion pattern and further radiates sound to the chair with a better disappearing act. Time to get new passives if you are picky, I think it will make a difference.

Corey [/quote]

I'm not too worried about it either way. The passives are there primarily to boost/extend bass response and better load the main driver. Secondarily, they add "ambient" midrange that is much lower in volume and in any case should bounce off room boundaries before coming to your ears. You really don't want direct radiated midrange from the passives going directly to your ears since it's liable to muddy up what's coming from the main driver. Now after bouncing off room boundaries it should be time-delayed enough to not muddy things but rather add ambient reverberation.

Brad, Grill covers would be nice, but I personally would be concerned that they would end up looking too obtussive and distracting. I want to keep the look of my cabinets as clean and sleek as possible. Having kids, though, I do understand the need for some kind of protection (Wow, that sounds like I was talking about birth control). The other thing I liked about my chrome ring idea is that it may make the passives look more like drivers and less like circular pieces of foam. The new passives, with thier multiple surround design is a step in that direction.

BTW does the dome on your new passives point to the inside? Is that what Corey is talking about? I personally would rather have them pointing in instead of out if its all the same for sound.

zinker the mdf on the outside is to clamp everything in place while you rout, otherwise the mdf circle inside the passive will fall into the cabinet The out side peace could be from anyold thikness of course and I only say MDF because I seem to have loads of it lying around

The man has all the answeres ziggy is right that is the easyest way. Itīs just that bits are expensive and if you dont have a rabbet bit and dont want to spend for one then the other way works for the straight bits. Cheap is my middle name you should see some of the home-made clamps I made to glue the HDTs together!

Btw, my passives look to be in backwards. Although both sides are "domed" the larger dome is on the inside. This really irritates me since they did not come with any directions - and logic told me that you don't want some big dome sticking outside the cabinet.Still, I wonder if it makes any sonic difference? Ziggy?

Thanks for the link Brad but I never buy cheap router bits, Cheap routers yes but the router bit is the important ībitī(so to speak) unless you throw them away after use. I would never use a cheap/dull bit on veneer(even my cheapness has limitations) As for the dome sticking the wrong way I thought you were pleased with the sound of the new passives so why change it If it ainīt broke....

P.s I built the all of the HDTīs using just 2 quality router bits and a cheap no-name router /my Hitachi was at the shop

Yes, A rabbit bit with a bearing would work, but I want to open up the rabbited area from the current 1/4" rabbit cut to a 1/2" cut. This will give me a wider area to use for screwing down a metal ring that I want to glue to the passive assembly(thus making the whole thig removable). I figure that if I use #6 flathead machine screws I will need the ring to be around 1/2" to allow for the countersunk holes. Also I need the additional room for the tee-nuts on the inside of the cabinet.

What I would need is a bearng bit that will cut a 1/2" wide rabbit cut. Do they make that size? My company's shop doesn't have one, but I would spring for one if it can be bought for under $35.

I've used the cheap chinese router bits. I think they're fine for garage weekend warrior types like many DIY speaker builders. Of course they won't last if you're a pro or frequent user, but then again you can buy new bits for the price of having good ones sharpened.

I am building my HDTs right now. I am incorporating the MK I alternate tuning. I have the information about the egg crate foam pieces as described in the kit docs. Does it make any sense to do more foam in the chambers than the kit mentions? Since I have the units fully accessible to the internal chambers, now would be a good time to know this.

Or are there any other treatments I should consider before sealing them up for 'eternity' ?

I wouldn't add any other foam other than whats on the paper, we tried everything we could think of last winter and thats where Steve thought it to be the best. In my opinion, for the Fostex driver, the Alt tunning can't be beat, except by adding the gell coated driver which is just putting icing on the cake.

On the other hand the HDT MKII has nothing in the cabinet. It doesn't need anything which is how the originial was when Steve first designed it. It only took 6 years for the first one.

I was admiring my alternate tuned passives in the sunlight today and am amazed at how responsive they are to light touch. With no music playing, just very gently brushing one with an absolute minor touch causes the other one to respond immediately. Tapping one causes the other to jump with a large amount of excursion. You need to have a bright light or sunlight shining on the one you are looking at to see just how responsive this is. I don't know if these have broken in more but I am amased how quick and how light a tap is "mirrored."

Completed the Alternate tuning kit and gelled driver upgrade last week. Thanks Bob, Steve and Devon for all your help in rectifying the shipping damage that unfortunately occured. I appreciate your quick efforts to resolve, and Bob I appreciated all the kind help you provided me to walk thro the mods. (I finally coaxed the fostex drivers out of their tacky home!!)

This mod definitely improves the speakers tonal balance, improves bass speed and articulation, the speakers do disappear more and soundstaging is better (I heard something outside my right speaker yesterday, that was cool).

The mod is fresh, so difficult to provide any full reports, but important to note that the above listening was done with a solid state belles amp and adcom pre. I had not enjoyed this combo with the stock HDT's for the last 2 months I've had them together. The fact is that the newly modded HDT's sound better than I ever expected them to with this SS combination (much more listenable and smooth than they did prior to upgrade).

I'm waiting for a new tube amp to arrive in the next few weeks, and I've bought some NOS bugle boys, mullards, and some cool rectifiers tubes to roll.

I originally had the stock HDT's with a Select and loved female vocals, loved its speed, but felt rock lacked bass foundation. I added an expensive / fast sub and it sounded pretty good.

Steve recommended the EX mod, which I completed and it did help the bass, however (as Steve said it would) it removed some of the air in the top end, and that was some magic I hated to lose.

Following the EX mod (and as the drivers burned in), I felt I started to enjoy the HDT's better without sub, so I began to run them more on their own.

I had plans to upgrade to Steve's new Torii Mk2 in anticipation of potentially increasing the choices of speaker models that I could audition and own, and I sold the EX to ready myself for the upgrade. At about the same time, however, the HDT Alternate tuning kit came out, so I decided to do that first to see if I had really heard the full potential of the HDT's, and am glad I did.

I had the Belles and Adcom on hand so have been using them in the interim, and again, am surprised how listenable (after such a short period of breakin) the system has become.

I will try to post again after new amp, new tubes, and some burnin has occured.